The present invention relates to a self-adhesive heat dressing for use in local treatment of skin and body areas.
Heat is widely used for treatment of minor nuisances, such as infiltrations and muscular tensions.
In most cases, the heat treatment is capable of removing or minimizing these nuisances by a relatively short treatment. Heat is also used as an analgesic e.g. for menstrual pain. Heat treatment is particularly important for treatment of rheumatism. Rheumatism cannot be cured, but the heat treatment can ease the worst pain.
Heat treatment has also been found to have significant effect for reducing skin lesions, such as e.g. psoriasis plaques. An article by Harukuni Urabe, MD, Keiko Mishitani, MD, Hiromu Konda, MD: Hyperthermia in the Treatment of Psoriasis. Arch. Dermatol.--Vol. 117, December 1981, pp. 770-774, mentions an experiment in which psoriasis has successfully been treated with heat.
The treatment lasted for 13-53 days. The heat dressing was changed 2-3 times a day, and in each period the skin temperature was raised to between 42 and 43.degree. C., which temperature was maintained for more than 2 hours.
For many years it has been known that the temperature is of great importance for regeneration of tissue, and thus also for the healing process in a wound area. In particular, attention has been given to the fact that a lowered temperature in a wounded area causes reduced metabolism and consequently reduced wound-healing. This is in complete agreement with the knowledge that when transplanting tissue the greatest success is achieved when the tissue graft has been cooled during the process. By cooling and consequent reduced metabolism, the life time of the tissue is thus increased.
Over the last few decades occlusive treatment of wounds has been increasingly used, and everything indicates that within not too long a time occlusive treatment of various kinds of wounds, such as burns, operative wounds, bed sores, leg sores, and diabetic wounds, will be the most commonly used method of treatment.
The great success of the occlusive method of treatment is largely due to the moist wound environment, which a number of examinations have shown i.a. causes an increased migration of epithelial cells. More recent experiments have, however, shown that the isolating effect of the occlusive method of treatment also plays an important part for the wound-healing. By occlusive treatment, the treated skin and wound areas are isolated, which may result in a slight increase in the surface temperature of the skin and wound areas. Thus, it is not an active heating, but only a shielding, whereby the heat loss from the surface of the skin and wound areas is minimized.
In spite of the fact that there is thus an indication that the temperature in a wounded skin area has significant influence on the healing process, and that by raising the temperature it is possible to increase the speed of healing, use of sustained heat for local treatment of wounds has as far as known not yet been used in practice.
For such nuisances in body and skin areas which it is known to treat with heat, the heat is usually applied by heat ray impact. It is often a matter of heat treatment of larger body and skin areas, but also local heat treatment is performed by means of heat rays.
Treatment with heat rays can, however, only be performed within the framework of hospitals or clinics, and is furthermore very expensive both as regards equipment and staff costs.
Usually the heat treatment must be performed several hours daily to obtain an efficacious effect. In particular when treating rheumatism and, which has been found at a later date, when treating wounds, a continuous treatment is required.
Thus, it is not only very expensive but also exacting on the patients' patience each day to have to go through hours of treatment with heat rays.
Another commonly known method of heat treatment is treatment with heat bags or heat pads. This mode of treatment is used in particular for minor nuisances, and the treatment is most frequently prescribed by the patient himself.
Heat pads generally consist of a pad of synthetic material with inlaid electric resistors in which the heat is generated by connection to the mains. Heat pads are used most frequently for menstrual pain and for milder forms of rheumatism. By treatment with heat pad, the patient, as in the case of treatment with radiation heat, is forced to sit or lie still for the duration of the treatment.
Heat bags may also be electrically heated, but most often they are chemically heated. The chemically heated heat bags consist of an oxygen-permeable bag containing a metal powder which oxidizes upon contact with oxygen, whereby heat is generated. Generally, metals, such as iron, aluminium or magnesium, are used, and in particular in the form of porous powders. The metal powders are usually mixed with catalysts and assistants, such as chloride ions and active carbon, as well as fillers and moisteners, such as bentonite and cellulose compounds. Heat bags of this kind are well known, and further mention hereof can be found e.g. in U.S. Pat. Nos. 4,282,005, 4,268,272, 4,106,478, 4,516,564, and 3,976,046, and in DE public disclosure No. 3 404 654 and DE patent specification No. 3 649 115.
The existing heat bags of the above type are especially used for treatment of infiltrations and sports injuries and as heat aggregate for people staying outdoors for quite a long time.
The heat bags are not particularly well-suited for use directly against the skin, since the heat development can be difficult to control. The skin is very heat-sensitive. Experiments with local heating of the skin have thus shown that heating of a skin surface area of 1 cm.sup.2 to a temperature of above 43.degree. C. for a prolonged period can cause severe burns. The temperature is especially critical in skin areas with impaired blood flow. The skin temperature is by treatment with a heat bag furthermore dependent not only on the amount of heat supplied, but also on the skin's own temperature, blood flows in the skin area, and the temperature of the surroundings.
Some of the known chemically heat generating heat bags are shaped as plane dressings which essentially have the same thickness throughout the entire extension of the dressing. This somewhat alleviates the problem, since the heat generating metal powder in such a heat dressing is evenly distributed over the entire area of the dressing.
By futher control of the air supply, chemically heat generating dressings have thus been achieved which in one surface area of the entire heat dressing essentially gives off a uniform amount of heat.
In spite of a uniform heat emission, a heat dressing placed directly against the skin can all the same give rise to local superheating, and consequently burns on the skin.
As mentioned above there are several factors influencing the skin's surface temperature by treatment with a heat dressing.
A particularly significant factor is the condition of the skin, and in particular the blood flow in the areas is of great importance.
A heat dressing having a surface area of e.g. 100 cm.sup.2 will thus cover skin areas with essential differences in blood flow. In the very local areas with a low blood flow, a heat agglomeration can thus easily occur, so that the temperature in these areas exceeds the average contact temperature of the heat dressing.
Patients with rheumatism are mostly older people whose blood flow, in particular in the outer skin layers, is impaired. Similarly, the blood flow in wounded skin areas, in particular in case of leg sores, is often considerably reduced.
When treating such patients with a heat dressing, there is thus a particularly large risk of local superheating of the skin, and consequently risk of burns.
Another essential cause for local superheating is the poor or defective contact between the heat dressing and the treated skin surface, in particular if the treated surface is essentially curved.
If the heat dressing is only in contact with the skin surface in part of the surface area of the dressing, the heat is essentially transferred to the skin surface area which is in contact. Since the heat given off from the dressing is independent of the contact area of the dressing, the skin surface area which is in contact will be supplied with more heat than intended, whereby the area easily becomes superheated.
In a treatment with a heat dressing, the dressing is usually placed "loosely" on the area of treatment, which causes the patient great nuisance since he must necessarily sit of lie still for the duration of the heat treatment.
However, a few dressings are known which can be attached by means of attaching bands. These dressings, however, can only be used for treatment of skin areas on arms and legs, and furthermore the attachment is not very stable, and the dressing is very liable to get displaced or fall off completely when the patient moves.
EP patent application No. 376 490 discloses a heat dressing consisting of a flat bag containing iron powder and water retaining agents. One of the bag sides is air-permeable, and the other bag side is provided with a thin layer of an acrylic adhesive which enables the heat dressing to be attached to clothing or directly to the skin surface.
Acrylic adhesives are normally considered skin-friendly adhesives and are widely used for plasters and microporous tapes which are moisture-penetrable. Heat dressings of the above type have, however, been found to cause significant skin nuisances when placed directly on the skin.
The heat dressing with acrylic adhesive causes in particular substantial skin irriration in the form of itching, smarting, and prickling in the skin surface, but by use of a heat dressing provided with acrylic adhesive directly on the skin also pronounced maceration, increased bacterial and fungal growth, and considerable changes in the skin's pH-value will be noted.
As mentioned above, the heating of the skin causes significant changes in the metabolic processes of the skin tissue. The changes i.a. cause increased excretion of liquid and waste substances through the skin, and the skin's sensitivity to exogenous impacts is generally increased.
These factors presumably are the reason why positioning of the dressing known from the EP patent application directly on the skin causes the above skin nuisances.
DE public disclosure No. 3 434 292 discloses another self-adhesive heat dressing which either on the entire surface facing the skin or in an edge area is coated with an adhesive. However, nothing is said about which adhesives may be used, and further it is stated as patentable measure that the surface facing the skin is coated with an analgesic. This analgesic may give further rise to the patient getting burnt by the dressing, since the patient, because of the skin's nerve endings being "unconscious" will not react as quickly in case of a local superheating.